There are many applications in, for example, medical, scientific and engineering fields, where data acquired from multiple sources must be correlated so as to facilitate the determination of, for example, temporal relationships between events recorded in the data from the different sources. It is common to digitize and record these data according to discrete sampling periods. Data from the various devices and other equipment might be recorded using video/audio tape recorders and other equipment. Each piece of equipment would be connected, if necessary by way of a suitable interface, to a host or control computer which would control the equipment to collect and record data about events occurring during an experiment or a predetermined study period. The data would then be analyzed to determine, for example, the subject's responses to certain events occurring during the experiment or study period.
Some of the events may occur at irregular intervals with respect to each other and the sampling period, while other events may occur periodically but asynchronously with respect to each other and the sampling period. For example, in kinesiology experiments, events may be generated by electronic devices such as stimulators which operate autonomously producing events which are asynchronous with respect to the frame rate of the video camera. This makes it difficult to study the time course of the response of the system because the input event may have occurred at any time during the course of the video frame to which it is ascribed.
Several of the devices may each have an inherent frame rate which must be preserved, but which may not be compatible with each other (e.g. video and motion analysis systems employing North American NTSC and European PAL video formats) or may not provide adequate temporal resolution for digitizing data acquired simultaneously from other sources. Other items of the equipment might have their own internal time base, or no time base at all. Some equipment might use footage meters, others elapsed time, and others count sampling intervals. To find a particular portion of data may involve searching for sync pulses like tone pips and light flashes, which is tedious and often not reliable. Consequently, with such an assemblage of equipment, problems arise during analysis of the data when trying to determine what temporal correlation, if any, exists between events recorded by different ones of the monitoring devices.